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SubjectRe: [PATCH] fortify: Avoid shadowing previous locals
On Mon, Oct 25, 2021 at 02:37:28PM -0400, Qian Cai wrote:
> __compiletime_strlen macro expansion will shadow p_size and p_len local
> variables. Just rename those in __compiletime_strlen.

They don't escape their local context, though, right? i.e. I don't see a
problem with the existing macro. Did you encounter a specific issue that
this patch fixes?

-Kees

>
> Signed-off-by: Qian Cai <quic_qiancai@quicinc.com>
> ---
> include/linux/fortify-string.h | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index fdb0a74c9ca2..155c622e4f24 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -10,18 +10,18 @@ void __read_overflow(void) __compiletime_error("detected read beyond size of obj
> void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
> void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)");
>
> -#define __compiletime_strlen(p) \
> -({ \
> - unsigned char *__p = (unsigned char *)(p); \
> - size_t ret = (size_t)-1; \
> - size_t p_size = __builtin_object_size(p, 1); \
> - if (p_size != (size_t)-1) { \
> - size_t p_len = p_size - 1; \
> - if (__builtin_constant_p(__p[p_len]) && \
> - __p[p_len] == '\0') \
> - ret = __builtin_strlen(__p); \
> - } \
> - ret; \
> +#define __compiletime_strlen(ptr) \
> +({ \
> + unsigned char *__ptr = (unsigned char *)(ptr); \
> + size_t ret = (size_t)-1; \
> + size_t ptr_size = __builtin_object_size(ptr, 1); \
> + if (ptr_size != (size_t)-1) { \
> + size_t ptr_len = ptr_size - 1; \
> + if (__builtin_constant_p(__ptr[ptr_len]) && \
> + __ptr[ptr_len] == '\0') \
> + ret = __builtin_strlen(__ptr); \
> + } \
> + ret; \
> })
>
> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> --
> 2.30.2
>

--
Kees Cook

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